The invention relates generally to vortex-type flowmeters which act to convert fluidic oscillations to corresponding mechanical vibrations which are transmitted to an outside coupling head engaged by an external force sensor whose signal is indicative of the flow rate of the fluid being metered, and more particularly to a flowmeter arrangement in which the mechanical vibrations are amplified in the course of transmission to increase the signal level of the sensor and to improve the frequency response of the sensing system.
Artificial lift expedients are often required to increase oil recovery at oil well sites. One widely used form of secondary recovery is the water-flood technique wherein pressurized water is forced through an injection well adjacent the site of the producing well, the injected water flooding the oil bearing region and providing the necessary pressure for oil extraction.
In a secondary recovery system, oil intermingled with water is yielded by the producing well. The water is thereafter separated from the oil and is returned to injection pumps delivering water to several injection wells, so that the secondary recovery system involves a network of water lines leading to a group of functioning wells. Waterflood techniques are also currently in use in uranium mining.
In maintaining and servicing a waterflood system, it is necessary to periodically check the water flow rate at various points in the water line network. The present practice is to effect measurement by means of turbine meters installed in the water lines. In the conventional turbine meter, the turbine rotor is mounted within the flow conduit, a permanent magnet being incorporated in the rotor. The rotating magnet induces an alternating-current in a pick-up coil located in the external housing of the meter, the frequency of the generated signal being proportional to the volumetric flow rate. The frequency of the signal is converted into a reading of flow rate.
Since turbine meters are relatively expensive, and a waterflood system requires a large number of such meters, one recent innovation has been to omit the pick-up coil from the meter and to provide a separate pick-up coil coupled to a battery-operated test set which affords a flow rate reading. This practice is feasible since it is only occasionally necessary for an operator to check flow rate at the meter installation and then, if necessary, to make a manual valve adjustment to correct flow rate. Thus the operator who carries the pick-up coil and the test set makes a tour of the various turbine meter installations to check the flow rate.
The main drawback of turbine flowmeters in the context of a waterflood system is that because it has a rotor which is exposed to the water, there is a reliability problem, in that the water being measured is often dirty and tends to foul and degrade the rotor and its bearings, particularly if the water contains abrasive particles and corrosive chemical constituents. Hence after prolonged use, the turbine meter may become inoperative or inaccurate.
In the above-identified copending application, there is disclosed a vortex-type flowmeter adapted to operate in conjunction with an external sensor coupled to a portable digital read-out device whereby the same external system may be used to take readings from a large number of installed flowmeters. The installed flowmeters are therefore altogether devoid of electrically-powered devices so that no danger exists in environments that cannot tolerate unattended electrical circuits.
The flowmeter disclosed in the copending application includes a flow tube forming a passage for the fluid to be metered and an obstacle assembly disposed in the tube and capable of generating strong fluidic oscillations which cause a deflectable section of the assembly to vibrate at a corresponding rate, the deflectable section being cantilevered by a flexible beam from a fixed section. Disposed within the beam is a rod which is caused to vibrate at the same rate as the deflectable system, the rod vibration being transferred to a probe placed within a passage in the fixed section of the obstacle assembly and extending to the exterior of the tube, whereby the vibrations of the deflectable section within the flow tube are transmitted to the exterior thereof.
The probe extension terminates in a coupling head outside the flow tube which is engageable by a force sensor adapted to convert the probe vibration into an electrical signal whose amplitude is proportional to the applied force and whose frequency is a function of flow rate. The force sensor is coupled to a test set serving to convert the signal into a flow rate reading. Such meters will hereinafter be referred to as external-sensor vortex-type flowmeters.
In the vibration transmission arrangement disclosed in the copending Herzl application, one end of the probe is anchored, the probe passing through a bore in the fixed section of the obstacle assembly and then through an opening in the wall of the flow tube, the other end of the probe terminating in the outside coupling head. The vibrating rod which is at right angles to the probe is linked thereto at a junction point intermediate the coupling head and the anchor point, whereby the probe is caused by the vibrating rod to swing about the anchor point acting as a fulcrum.
The force exerted on the force sensor by the coupling head and the amplitude of the resultant signal depends on the mechanical advantage afforded by the probe of the vibration transmitter. Mechanical advantage represents the ratio of the force exerted by a device to the force acting on it. Thus if the handle of an automobile jack is moved 1 inch in lifting a car 0.002 inches, the mechanical advantage is 500. In the present context, the larger the mechanical advantage, the greater the amplification of the applied force applied to the sensor.
In the vibration transmitter, the probe functions as a lever, one arm of which is that portion of the probe which extends between the junction point of the rod and probe at which a force is applied (rod arm), the other arm being the remaining portion of the probe extending between this junction point and the coupling head (coupling head arm). The mechanical advantage of a lever is determined by the ratio of its arms, and since in the vibration transmitter disclosed in the copending Herzl application, the rod arm is somewhat shorter than the coupling head arm, the mechanical advantage is less than one.
As a consequence, the force exerted by the coupling head on the force sensor is less than the force derived from the deflectable section and applied to the probe. The amplitude of the resultant sensor signal is therefore quite low. Because of this low level sensor signal, the signal-to-noise ratio is unfavorable and the system associated with the sensor has a frequency response which is less than satisfactory.